At El Zota Biological Field Station in northeastern Costa Rica, J. Alan Clark, Ph.D. wakes before dawn each morning and slogs several miles into the rainforest before the curtain of sunlight rises, setting off a chorus of birdsong.
But it is the song of one particular species that is music to his ears.
Clark, an assistant professor of biology at Fordham, and his co-researcher, Nigel Mann, Ph.D., professor of biology at SUNY Oneonta, have honed in on a group of stripe-breasted wrens whose songs don’t fit the normal duet pattern among their genus.
There are some 75 species of wrens, and many of the males and females sing a “call” to each other to mark discrete territories and mating availability. But the complex duet pattern among the striped wrens, which involves an extra set of calls, or owl-like “hoots,” baffles the researchers.
“Most wrens have complicated songs that they duet, but these wrens are kind of weirdos within their genus,” Clark said. “Very little is known about the species to start with, let alone what evolutionary forces might have caused them to develop this second set of calls. We also don’t know whether it’s just the males or the females [as well].”
The stripe-breasted wrens live in the middle canopy layer of the rain forest, higher up than most similar songbirds. The researchers’ working hypothesis is that the birds’ elevated habitat led them to adopt a second set of calls to deal with a different suite of predators.
Another possibility, according to Clark, is that sound travels differently higher in the rainforest canopy, requiring more calls.
“The location definitely makes the species harder to see and harder to study,” Clark said, noting that it rains daily and that the scarcity of the birds has made it a challenge to reach the required number of target males.
To study the song’s significance, the team marked birds with different colored bands, mapped each group’s territory and recorded their songs.
Now they are doing a series of playback experiments to chart which bird behavior goes with what song. Like most birds, wrens maintain discrete territories for breeding purposes. Within those areas are “singing posts,” said Clark, where birds announce, “’This is my territory, and I am here—single and sexy.’
“The dueting part of these species is a very good model for how the sexes cooperate or don’t cooperate,” he said.
Bird singing, Clark said, has become a model for a lot of research on how other species communicate. Therefore, the project may even produce findings that can be applied to research on how human beings learn language.
“Like humans, songbirds actually learn their songs,” Clark said. “It is much easier to study how a bird learns its song than it is to study human babies, because of the ethical issues and because birds learn songs in weeks rather than in years.”
This fall, Clark will head to Panama to study a relative of the stripe-breasted species, the stripe-throated wren.